Princess Royal

Princess Royal is a title often given by the reigning British King or Queen to his or her eldest daughter. The title is a gift of the monarch, unlike Prince of Wales which is always given to the eldest son

There can only be one Princess Royal at a time, so Elizabeth II never held the title because her aunt, Princess Mary was already called Princess Royal.

Before Charles II in 1660 started using the title of Princess Royal, the eldest daughters of the King of England had a special status. The Magna Carta made the Barons to pay for the eldest daughter's wedding,[1] and later sleeping with her was made High Treason,[2] punishable by death - a law only changed in 1998 [3]